For gene expression products, a variety of analytical methods are known. For instance, methods that use in situ hybridization, fluorescence resonance energy transfer, loss of fluorescence polarization, and the like may be cited. In these various analytical methods, while probes, primers and the like for detecting specific base sequences are used, the characteristics required of the probes or the like are different depending on the purpose of the analysis.
So far, nucleoside derivatives with a variety of modifications or alterations have been developed, in probes or the like for detecting specific base sequences. For instance, peptide nucleic acid (PNA) and bridged nucleic acid (BNA) may be cited. In addition, various open sugar ring-type nucleotide derivatives have been reported (Non-patent References 1 to 7). In addition, ring expansion-type modifications in the bases have also been attempted (Non-patent References 8 and 9).    Non Patent Reference 1: P. E. Nielsen, M. Egholm, R. H. Berg, O. Buchardt, Science, 254, 497 (1991).    Non Patent Reference 2: S. Obika, D. Nanbu, Y. Hari, J. Andoh, K. Morio, T. Doi, T. Imanishi, Tetrahedron Lett., 39, 5401 (1998).    Non Patent Reference 3: K. C. Schneider, S. A. Benner, J. Am. Chem. Soc., 112, 453 (1990).    Non Patent Reference 4: K. Augustyns, A. V. Aerschot, A. V. Schepdael, C. Urbanke, P. Herdewijn, Nucleic Acids Res., 19, 2589 (1991).    Non Patent Reference 5: M. Azymah, C. Chavis, M. Lucas, F. Morvan, J.-L. Imbach, Nucleosides & Nucleotides, 11, 1241 (1992).    Non Patent Reference 6: P. Nielsen, F. Kirpekar, J. Wengel, Nucleic Acids Res., 22, 703 (1994).    Non Patent Reference 7: L. Zang, A. Peritz, E. Meggers, J. Am. Chem. Soc., 127, 4174 (2005).    Non Patent Reference 8: N. Minakawa, N. Kojima, S. Hikishima, T. Sasaki, A. Kiyosue, N. Atsumi, Y. Ueno, A. Matsuda, J. Am. Chem. Soc., 125, 9970 (2003).    Non Patent Reference 9: H. Liu, J. Gao, L. Maynard, Y. D. Saito, E. T. Kool, J. Am. Chem. Soc., 126, 1102 (2004).